Recently, it has been reported that nitrogen monoxide (NO) is involved in lifestyle-related diseases such as diabetes, arteriosclerosis and cancer. More specifically, it has been reported that abnormality in NO production is involved in many physiological functions and diseases. For example, it is known that shortage of NO is responsible for hypertension, hyperlipemia, arteriosclerosis, heart failure, coronary spasm, etc., and that excess of NO is responsible for cerebral apoplexy, Huntington's disease, Parkinson's disease, etc.
On the other hand, NO is one of the environmental pollutant NOx, and development NO-scavenging materials is important in measuring environmental pollution and in purifying polluted air, water or the like.
Thus, development of materials for quantifying or scavenging NO has been desired.
However, NO is a gas and unstable at normal temperatures. Therefore, it is difficult to handle or quantify NO. Further, no effective NO-scavenging materials have been known to date.
The present inventors have already found that cytochrome c has NO-scavenging ability (Chemistry and Organisms, 34 (12), 784-786 (1996)). Also, the inventors have isolated similar C-type cytochromes from various organisms such as red alga Porphyra yezonesis, green alga chlorella and photosynthetic bacteria, and confirmed NO-scavenging ability in them (Biosci. Biotechnol. Biochem., 64(3), 628-632, 2000; Jap. J. Pharmacol., 75 (Suppl. I), p. 113 (1997)). Further, the present inventors have determined the tertiary structure of red alga Porphyra yezonesis-derived cytochrome c6 by three-dimensional structure analysis with x-ray (Acta Cryst., D56, 1577-1582 (2000)) and constructed an expression system for cytochrome c6 in a recombinant Escherichia coli. 
The present inventors have advanced further the research in materials having NO-scavenging ability, as a consequence they have found heme peptides having higher NO-scavenging ability than cytochrome c.